Elliptic spring.



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WILLIM G. PRICE, OF NEW CASTLE, PENNSYLVANIA.

ELLIPTIC SPRING.

Specification oi' Letters Patent.

Patented March 17, 1908.

Application filed August 18, 1906. Serial No. 33T 141.

To all lwhom it may concern:

Be it known that l, WILLIAM G. PRICE, a resident of New Castle, in the county of Lawrence and State ol" Pennsylvania, have invented a new and useful Improvement in Elliptic Springs; and l do hereby declare the following to be a full, clear, and exact de-4 ,scription thereof. l

This invention relates to elliptic springs; and especially to such springs for use sup-l porting the bolsters of motor car trucks and the like.

rl`he object of the invention is to provide an elliptic spring sufficiently strong to carry the heavy weightof modern motor cars, and one which at the saine time is easy riding.

In electric motor trucks as at present designed it is desirable to use a narrow bolster. rlhis necessitates the use of narrow elliptic bolster springs and in order to carry the heavy cars these springs must have a coinparatively large number of leaves, at least six or eight being required,

lt ,is well known that when an elliptic spring oscillates the leaves which rest upon each other slide one upon the other to a slight extent, thus producing friction which retards movement ofthe spring and brings the oscillations to rest. ln other words the friction absorbs the energy of motion so as to slow down and stop the oscillations. This is called the damping effect of elliptic springs. Wvhen more than four leaves are in Contact the damping effect becomes so great that the oscillation of the spring is checked very quickly and consequently the spring becomes hard riding. This can be explained as follows: ln a properly designed elliptic spring, cach leaf carries an equal proportion of the load. Suppose that we represent the load carried by each leaf t-o be pounds. Consequently thel outer leaf presses upon the :'ocond leaf with a pressure of 100 pounds, the second loaf presses upon the third with a pressure of )00 pounds plus l0() pounds, or 2U() pounds, while the third presses upon theI fourth with a pressure of pounds, and so on continuously vthrough the number of loaves in the spring. ,lt is well known that the friction of two smooth surfaces m sliding cmitact varies 'in direct propia-tion to the weight which presses or holds thosc surfaces ir. ront'act, and does not depend upon the extent of surfaceyin contact. The co-eflicient of friction between steel plates such as elliptic springs are ordinarily made of is approximately 20 per cent. of the pressure.

t will be readily understood from the foregoing that the frictional resistance against the oscillation .of the spring, in other words, the damping elfect'of the spring, increases aritlnnetically according to the number of leaves composing the spring and in contact with each other. Consequently a spring having the required number of leaves ,to carry modern .heavy cars has a very high damping (zo-efficient and becomes a hard riding spring.

The object of this invention is to [provide a spring having a sufiicient number lof leaves of the narrow width required .for electric motor trucks to carry modern heavy cars, but which. nevertheless is an eas riding spring, or in other words, is a spring l laying ,a low damping (ip-efficient. his object issecured by dividing the spring, or the leaves vof the spring, into groups so that not more than three of the leaves .consecutively are in contact, thus in effect providing a plurality Of independent springs each having a'low damping co-efficient.

The invention also consists in making the inner spring of lighter metal than the outer spring', in order to provide equal fiber strains throughout;

In the accompanying drawings Figure l is a side view of a spring constructed according to my invention; Fig. 2 is a plan view there'- of; and Fig. 3 is a view of one end of a spring showing a modification..

The spring shown vin the drawing is a double spring as seen in Fig. 2, each spring being composed of six leaves divided into an outer group, and composed of three leaves numbered 1, 2 and 3, respectively; and an inner group of a similar number ofileaves numbered di, 5 and (i, respectively. i Each of these groups has leaves of varying lengths as shown, and said leaves are connected at their middle portions by the usual bands 7. These groups constitute in effect two se )arate elliptic springs, the outer one being longer than the inner one. The ends of the longest leaves 3 of the outer spring are in Contact and united to each other by means of the bolts 8, while the ends of the longest leaves 6 ol` the inner spring are preferably out of contact with each other when the spring is not under load, as shown at 9, Fig. l, although they may be in contact with each other as .2 shows a double spring having two sets of connecting bolts 8.

`second on the third,

i i l l the -fifth, 400 pounds, and of the iifth on the r sixth, 500 pounds, or i constructed as shown in the drawings. The iresult is that my spring is an easy riding spring, While the other spring is a very hard riding spring.

inasmuch as the inner spring is shorter than the outer spring, it Works on a shorter leverage and consequently if the leaves were of the saine thickness as those of the outer spring, the fiber strains on the inner spring would be the greater. To avoid this it is necessary to make the inner spring either of a weaker meta-l or, what is more practical, make it of thinner plates than the outer spring, so that when compressed the fiber strain will be uniform throughout. 'The drawing shows the leaves of the inner spring l thinner than those ot the outer spring.

TWhile I have shown the invention aiplied to a spring having two groups of three leaves each, it will be apparent that it can be applied to a spring having any reasonable number of groups, each group composed ofany reasonable number of leaves.

/Vliat claim is:

An ellipticI spring comprising a plurality of complete springs each composed of a plurality of leaves, said springs being placed one Within the other and being in contact only at their iniddles, the leaves of the inner spring or springs being thinner than those of the outer spring.

In testimony whereof, I, the said VILLIAM G. PRioE have hereunto set my hand.

- VVLLAM G. PRICE.

`Witnesses M. D. VOGEL, F. W. WINTER.

shown at 10, Fig. 3. To permit the ready l assembling of the springs, however, the construction shown in F ig. l is preferred. Fig.

springs side by side and united by the end It will be observed that only three of the sin: leaves composing the spring are in coni tact consecutively. The leaf 4 of the inner group is of couple incontact with the leaf 3 i of the outer group, hut this is only at the ,l middle portion and the taper of the short j leaf 4 is such that these groups contact practicaliy only at the spring and, at Whichi point there-is practically no sliding movef ment one on the other. The result is that i the damping eiTect of each group or' springs i is limited to two consecutive contacts. l instance, the leai` l presses on the leaf 2 with 100 pounds pressure, and the leaf 2 presses J on ythe leaf 3 with 20() pounds pressure, niaking a total for the group of 300 pounds. As i the friction is approximately 20 per cent. of ,l this, it amounts to 60 pounds. `'ihesame l holds true with reference tothe inner group, l so that the total friction or damping eiiect l for the spring is 120 pounds. If, now, the spring were made up of six leaves ail in contact With each other, the pressure of the iirst on the second would be 100 pounds, ol the 20G pounds, of the thirdV on the fourth, 300 pounds, of the fourth on a total of 1500k pounds; Twenty per cent. of this is 300 pounds, so that the damping eii'ect would be two and onehalf tinies the damping effect of a spring having the saine carryingcapacity when 

